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K.H. Al-Juboory, D.J. Williams, and R.M. Skirvin

Shoots of greenhouse-grown Algerian ivy (Hedera canariensis L.) were surface disinfected and explanted on modified Murashige and Skoog (MS) medium supplemented with BA (10 μm) and NAA (2.5 μm). One month later the shoots were transferred to MS proliferation medium supplemented with TDZ (0.1 or 0.5 μm) and NAA (40 μm). An average of three microshoots developed on each stem treated with TDZ. Pruned shoots grown on MS medium supplemented with GA3 (20 μm) and BA (20 μm) branched better than unpruned shoots (3.7 vs. 1 per explant, respectively). Rooted shoots grown ex vitro grew and developed a shape suitable for commercial sale in 3 months. Chemical names used: N -(phenyl-methyl)-l H -purine-6-amine (BA); gibberellic acid (GA3); 1-naphthaleneacetic acid (NM); N -phenyl-W-1,2,3-thiadiazo-5-yl urea (Thidiazuron, TDZ).

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Xiaoling Yu and Barbara M. Reed

A micropropagation system was developed for hazelnut cultivars. Grafted greenhouse-grown plants produced many more viable explants than upper branches of mature field-grown trees. Shoots from grafted greenhouse-grown plants collected March through July and suckers of mature field-grown trees collected in July produced the most growing explants (46% to 80%). Three- to five-fold multiplication was obtained after 4 weeks of culture on NCGR-COR medium supplemented with 6.7 μm BA and 0.04 μm IBA. Roots were produced on 64% to 100% of shoots grown on half-strength NCGR-COR mineral salts and 4.9 μm IBA for 4 weeks. Ex vitro rooting by a brief dip in 1 or 5 mm IBA was equally successful. Transplant survival was 78% to 100%. Chemical names used: N 6-benzyladenine (BA); indole-3-butyric acid (IBA).

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M.T. Vidal, C. Azcón-Aguilar, J.M. Barea, and F. Pliego-Alfaro

Micropropagated plantlets of avocado (Persea americana Mill.) exhibit a very slow rate of growth during the acclimatization phase, possibly because mycorrhizae are absent. Inoculation of plantlets with the vesicular-arbuscular mycorrhizal fungus Glomus fasciculatum (Thaxter sensu Gerd) Gerd and Trappe improved formation of a well-developed root system that was converted into a mycorrhizal system. Introduction of the mycorrhizal fungus at the time plantlets were transferred from axenic conditions to ex vitro conditions improved shoot and root growth; enhanced the shoot: root ratio; increased the concentration and/or content of N, P, and K in plant tissues; and helped plants to tolerate environmental stress at transplanting. Inclusion of soil as a component of the potting medium appeared to favor mycorrhiza formation and effectiveness. Thus, mycorrhiza formation seems to be the key factor for subsequent growth and development of micropropagated plants of avocado.

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A. M. Richwine, J. Tipton, and G. Thompson

Hesperaloe parviflora is a useful xeric landscape plant. Two methods of shoot culture initiation were developed. Shoots were initiated indirectly through the use of callus derived from pieces of young inflorescences. Callus was initiated on modified Murashige and Skoog medium with 4.52 μM 2,4-dichlorophenoxyacetic acid and 2.32 μM kinetin. Callus produced shoots when placed on modified MS medium with 6.0 μM zeatin riboside. Direct initiation of shoots was also accomplished using the bottom four floral buds of young inflorescences. Buds were placed on modified MS media containing either benzylaminopurine or kinetin at 0.1, 1.0, or 10.0 μM or zeatin riboside at 6.0 μM. The most shoots were produced by the medium containing 6.0 μM zeatin riboside. Preliminary results indicate optimum shoot production with 2.0 to 4.0 μM BA or 6.0 μM zeatin riboside.Hesperaloe parviflora micro-shoots were rooted on one quarter strength MS medium and ex vitro.

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Rida A. Shibli, M. Ajlouni, A. Jaradat, and M. Shatnawi

Some factors that affect the in vitro conservation of wild pear (Pyrus syrica) microshoot cultures were studied. Sorbitol and mannitol at 0.2 to 4.0 M reduced growth significantly and extended the subculture intervals to 5 months when cultures where kept at 15°C. Increasing sucrose to 12% in the medium was not highly effective and the subculture intervals did not exceed 3.0 months. After 2 years of maintaining cultures on slow-growth medium, cultures grew slowly when transferred to fresh control medium. Shoots started to proliferate after three subcultures (6.0 weeks apart) on medium containing 1.0 mg/L BA and 0.1 mg/L NAA. New microshoots were rooted on medium containing 2.0 mg/L IBA and rooted microshoots gave 90% survival when acclimatized ex vitro under intermittent mist.

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José M. Iriondo, Carmen Moreno, and César Pérez

Micropropagation methods for six rockrose species (Cistus albidus L., C. clusii Dunal, C. ladanifer L., C. laurifolius L., C. psilosepalus L., and C. salvifolius L.) were established. Cultures, initiated from nodal segments of seedlings, were grown on MS medium, alone, or supplemented with 0.88 μm BAP or 0.93 μm Kin. Multiple shoot formation was obtained after the first subculture (30 days) from which new nodal segments were taken and grown on the same culture medium to maintain proliferation. Shoots obtained at the third subculture were rooted alone or supplemented with different concentrations of IBA. The plantlets of the six species, thereby obtained, were successfully acclimatized to ex vitro conditions. Chemical names used: 6-benzylaminopurine (BAP), indole-3-butyric acid (IBA), 6-furfurylaminopurine (Kin).

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Issam A. Hassaballa, M.G. Moughieth, N.A. Hagagy, and N.S. Zayed

Shoot tip and single-node cutting explants of `Hamawy' and `El-Amar' apricot cultivars were initiated from forced shoots of field-grown, virus-free trees. Explants were cultured on Murashige & Skoog (MS) Nitsch & Nitsch and Anderson media. Different modifications of MS medium were also evaluated. Antioxidant pretreatment reduced phenolic compounds and decreased necrosis. Modified MS was the best medium for plantlets regeneration, with positive effectiveness of adenine sulfate addition to the modified MS. Shoot multiplication was best on 2.0 mg·L–1 BAP and 1.0 mg·L–1 thidiazuron (TDZ). Also, half-strength MS medium was superior for shoot elongation Surface coverage, 16 hours light/8 hours dark cycle, and 2.0 mg·L–1 IBA induced good rooting. Rooted plantlets were successfully acclimated ex vitro.

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John L. Edson, David L. Wenny, and Annette Leege-Brusven

Idaho's population of Pacific dogwood (Cornus nuttallii Audubon) has declined. Propagation of disease-resistant clones would be useful to horticulturists and conservation biologists. In vitro-derived microshoots, incubated for 1 month on woody plant medium supplemented with 6.04 mm calcium gluconate and 4.44 μm benzyladenine, produced an average of 3.1 axillary microshoots per explant. Up to 62% of the elongated microshoots had rooted ex vitro 5 weeks following a 4.5%IBA talc dip. Plantlets resumed shoot growth within 2 months of acclimatization, and 70% survived after 1 year. This protocol is more rapid and efficient than propagation by layering or rooting the difficult-to-root stem cuttings of this species. Chemical names used: 2,3,4,5,6-pentahydroxy-caproic acid (calcium gluconate), benzyladenine (BA), 3-indolebutyric acid (IBA).

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Dennis P. Stimart and John C. Mather

Cotyledons from developing embryos 6 to 8 weeks old of Liatris spicata (blazing star) were cultured on Murashige-Skoog (MS) medium containing 0, 0.4, 4.4, and 44.4 μ M benzyladenine (BA) or 0, 0.2, 2.2, and 22.2 μ M thidiazuron (TDZ) to induce adventitious shoot formation. The highest percent of cotyledons forming shoots with highest shoot counts was on medium containing 2.2 μ M TDZ. Vitreous shoots formed on medium with 22.2 μ M TDZ. Callus derived from cotyledons and cultured on medium containing 4.44 μ M BA or 2.2 μ M TDZ formed adventitious shoots with highest shoot counts on 4.44 μ M BA. Adventitious shoots derived from cotyledons and callus were rooted on MS medium with 5.0 μ Mindole-3-butyric acid, acclimatized and grown ex vitro. All micropropagated plants appeared similar to each other.

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Richard K. Kiyomoto and Mark H. Brand

Experiments were conducted on tissue proliferation (TP) development and in vitro and ex vitro growth of tissues from plants with (TP+) and without TP (TP-). In 1993 the increase in TP in one-, two-, and three-yr-old `Holden' and `Besse Howells' was 3%, 52%. and 32% and 10%, 26% and 21%, respectively. No differential mortality was observed. Shoot tip cultures initated from TP+ and TP- `Montego' showed 10-12 mo were required for miniaturiziation and multiplication in TP- shoot tips and 4 mo in TP+ shoot tips. TP- cultures require 10 uM 2-iP for normal shoot proliferation; whereas TP+ cultures had to be transferred to hormone-free medium after 6 mo to maintain normal shoot morphology. Cutting propagation from TP- and TP+ plants older than 5 yr, showed persistence of morphological aberrations associated with TP+ plants.